Can you use 1 python script for multiple GE scenes?
Can you use 1 python script for multiple GE scenes?


Yes, you can.

This has nothing to do with messages, or delays. Python is executed by a Python controller. A Python controller gets executed (as each other controller) either once or never within a single logic frame.

Messages

Messages will be transferred after the logic bricks are executed but before the next frame starts. From perspective of logic - between the frames.

That is the reason why it takes exactly one frame between sending and receiving a message.

Effect:


When you perform operations while sending a message and operations when receiving this message ... you will notify a one frame delay. 
If you do not want that, you should ensure all operations (except sending the message) react on the same event -> e.g receiving the message.



  ... how would I identify an object from a separate scene?


You can grab the scene and read the objects it has.